The invention is based on a motor-driven manual grinder, in particular an eccentric-plate grinder.
A manual grinder of this type is known (European Patent Disclosure EP 0 245 850 A2), in which the first rolling face is embodied as an outer annular gear, which revolves with the driven grinding plate about the axis thereof, and in which the second rolling face is formed of an inner annular gear on an external crown gear, which is retained in a manner fixed against relative rotation with respect to the tool housing and is adjustable axially, by means of an external actuating device, between an inoperative position and a functional position that cooperates with the first rolling face. In the inoperative position, the second rolling face is out of engagement with the first rolling face. In the functional position, conversely, the second rolling face extends in approximately the same diametrically opposed plane as the first rolling face, so that in the revolution of the grinding plate the first rolling face can roll along the second rolling face, and thus a motion that rotates the grinding plate about its eccentric axis is superimposed on the eccentric motion of the grinding plate. As a result, when the second rolling face is in the functional position, enhanced abrasion of the workpiece is attainable. A disadvantage of this manual grinder is that the repositioning between idling and the forced-drive mode is not possible during operation of the manual grinder. In the axial relative motion, damage can occur to the teeth of both rolling faces. Another disadvantage, because of this arrangement of rolling faces, is a relatively great structural height of the grinder.
The motor-driven manual grinder of the invention, in particular an eccentric-plate grinder, has the advantage over the prior art that a switchover between the free-wheeling mode and the forced-entrainment mode is possible during operation of the manual grinder without the risk of damage, and the structural height is reduced at little expense for gearing.
By the provisions recited in the other claims, advantageous refinements of and improvements to the motor-driven manual grinder defined by claim 1 are possible.
In an advantageous embodiment, the braking device has an eccentric lever, actuatable by hand, for instance, that actuates the brake member and that has an eccentric element acting on the brake member.
The eccentric lever can be supported pivotably in the tool housing and as its eccentric element can have an eccentric peg that engages an opening, for instance a loop, on the end of the brake member, especially a brake band, which loops around the outer circumferential face of the external crown gear.
In another advantageous embodiment, the eccentric lever has a handle, located outside the tool housing, for pivoting actuation. Advantageously, the eccentric lever can be designed such that tensing the brake band is done by means of pivoting about a circumferential angle of about 180xc2x0. Thus the handle of the eccentric lever can easily be pivoted between two positions on traversing a circumferential angle of 180xc2x0, and thus the repositioning between the forced-drive mode and the free-wheeling mode can be done even during operation of the manual grinder.
In another advantageous embodiment of the invention, the outer annular gear is a part, in particular an integral part, of the grinding plate unit, for instance an integral component of the grinding plate itself, onto which the outer annular gear is injection-molded. This is especially simple and economical and furthermore contributes to reducing the structural height.
In still another advantageous embodiment, the inner annular gear of the external crown gear has a higher number of teeth than the outer annular gear. The difference in the number of teeth can for instance be 2. As a result, in the establishment of the forced-drive mode, the grinding plate can be driven at a thus-specified rpm. For instance, if the number of oscillations is 10,000, then for a ratio of the number of teeth of 50:48, the resultant rotary speed of a grinding plate in the forced-drive mode is 417 rpm.
In another advantageous embodiment, the grinding plate unit has a sleeve, coupled and in particular connected in a manner fixed against relative rotation to the work spindle and having an eccentric peg, for instance on its end, as well as a grinding plate retained on the peg by means of a bearing and connected detachably, for instance by means of a screw, to the eccentric peg.
It can also be advantageous if the outer annular gear has a bearing ring, axially spaced apart from the inner annular gear along the center axis, and is rotatably supported with the bearing ring by means of a bearing relative to the sleeve that is coaxial to the work spindle. The bearing can for instance be pressed onto the sleeve, and the external crown gear is pressed with its bearing ring onto the outer ring of the bearing.
In yet another advantageous embodiment, a fan wheel of an internal dust extractor is secured to the sleeve. Alternatively, the fan wheel can also be seated directly on the work spindle in a manner fixed against relative rotation and can have a sleeve that is eccentric to the spindle axis, with a cylindrical sleeve for terminal retention of the grinding plate being rotatably supported in the eccentric sleeve by means of a bearing.
In another advantageous embodiment, the sleeve with the eccentric peg on its end is formed of a sintered part and is thus designed especially economically. It can also be advantageous if the external crown gear is formed of a lightweight metal or zinc die-cast part, which once again makes for an economical design.
In another advantageous embodiment, the grinding plate, with the outer annular gear integral with it and forming the first rolling face, is formed of a one-piece injection-molded part, making for still further cost reduction and simplification.
Yet another advantageous embodiment provides that the brake member can be locked relative to the tool housing in a first position, in which it is in positive engagement with the second rolling face, and in a second position, in which it is not in any engagement with the second rolling face. It is especially advantageously possible as a result that the braking device is switchable between the first and second position and vice versa in all operating states, and in particular during idling, at a stop, and under load.
It is especially advantageous if the brake member is a band, in particular a toothed belt, with a plurality of teeth which are able to enter into engagement with a crown gear of the second rolling face. Compared to purely frictional engagement, in this case no slip occurs between the braking device and the second rolling face. This prevents wear of the two parts meshing with one another and suppresses heat production.
It is especially advantageous if the brake member is embodied as an elastic band, in particular as a toothed belt. By means of such an elastic intermediate coupling, the switchover from the free-wheeling mode to the forced-entrainment mode can be made easily, with little tolerance.
Preferably, the brake member, in particular the elastic element, is connected to the tool housing at a fixation point such that it is rotatable about a fixed rotary axis. As a result, upon motion of the elastic element between the first and second positions, it is unnecessary to kink the elastic band, which means less wear.
It is advantageous if the braking device has a detent lever, which is connected to the tool housing via a spring element, especially if the spring element seeks to press the detent lever into a position in which the elastic element assumes its first position. Such a design is mechanically easy to achieve and is nevertheless sufficiently stable, so that incorrect operation will not occur.
It is also advantageous if the brake member is of spring-elastic material and has a first recessed region with a set of teeth, which can be brought into engagement with the outer circumferential face, and a second recessed region, and the brake member is held by prestressing in its first position and can be brought into its second position by an actuating device. It is possible as a result to use a simple part, such as a stamped part, as the brake member. This provides an economical embodiment. Moreover, by means of such a design, simple actuation is possible with an only slight actuating force. This embodiment simultaneously functions as an overload protection for the forced operating mode and as a cushion against rotational impact. It requires little space; in addition, it becomes possible to compensate for errors in pitch of the gear part, for instance caused by gear wear.
It is also advantageous if the detent lever is displaceable by means of an eccentric bolt, which is supported rotatably on the tool housing and is operable by means of the actuating device protruding from the tool housing. Thus the user can very easily switch over between the two positions of the elastic element without having to turn off the device, regardless of the operating state it is in at that particular time, that is both in the free-wheeling (fine grinding) mode and the forced-entrainment (coarse grinding) mode.
It is also advantageous if the fixation point and the eccentric bolt are essentially diametrically opposite one another relative to the central axis, and the angle between the fixation point and the teeth of the elastic element, which in the first position are in engagement with the second rolling face, is greater than 90xc2x0. This prevents overlooking under load.
It is furthermore advantageous if the fixation point and the eccentric bolt are essentially diametrically opposite one another relative to the central axis, and the cooperating faces of the brake member and of the second rolling face, under load, reinforce the retention force, similarly to a servo effect. Thus at little effort, a major retaining force is generated, which increases the reliability of the apparatus.
It is also advantageous if the braking device is switchable between the first and second position and vice versa in all operating states, and in particular during idling, at a stop, and under load. As a result, there is no need first to switch from one operating mode to another to enable switching between the first and second positions. This saves time and makes for greater ease of use for the user.
Further advantages and details of the invention are the subject of the dependent claims.